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MOUNT(8) Linux Programmer's Manual MOUNT(8)
NAME
mount - mount a file system
SYNOPSIS
mount [-lhV]
mount -a [-fFnrsvw] [-t vfstype] [-O optlist]
mount [-fnrsvw] [-o options [,...]] device | dir
mount [-fnrsvw] [-t vfstype] [-o options] device dir
DESCRIPTION
All files accessible in a Unix system are arranged in one big tree, the file hierarchy,
rooted at /. These files can be spread out over several devices. The mount command serves
to attach the file system found on some device to the big file tree. Conversely, the
umount(8) command will detach it again.
The standard form of the mount command, is
mount -t type device dir
This tells the kernel to attach the file system found on device (which is of type type) at
the directory dir. The previous contents (if any) and owner and mode of dir become invis-
ible, and as long as this file system remains mounted, the pathname dir refers to the root
of the file system on device.
Three forms of invocation do not actually mount anything:
mount -h
prints a help message;
mount -V
prints a version string; and just
mount [-l] [-t type]
lists all mounted file systems (of type type). The option -l adds the (ext2, ext3 and
XFS) labels in this listing. See below.
Since Linux 2.4.0 it is possible to remount part of the file hierarchy somewhere else. The
call is
mount --bind olddir newdir
After this call the same contents is accessible in two places. One can also remount a
single file (on a single file).
This call attaches only (part of) a single filesystem, not possible submounts. The entire
file hierarchy including submounts is attached a second place using
mount --rbind olddir newdir
Note that the filesystem mount options will remain the same as those on the original mount
point, and cannot be changed by passing the -o option along with --bind/--rbind.
Since Linux 2.5.1 it is possible to atomically move a mounted tree to another place. The
call is
mount --move olddir newdir
Since Linux 2.6.15 it is possible to mark a mount and its submounts as shared, private,
slave or unbindable. A shared mount provides ability to create mirrors of that mount such
that mounts and umounts within any of the mirrors propagate to the other mirror. A slave
mount receives propagation from its master, but any not vice-versa. A private mount car-
ries no propagation abilities. A unbindable mount is a private mount which cannot cloned
through a bind operation. Detailed semantics is documented in Documentation/sharedsub-
tree.txt file in the kernel source tree.
mount --make-shared mountpoint
mount --make-slave mountpoint
mount --make-private mountpoint
mount --make-unbindable mountpoint
The following commands allows one to recursively change the type of all the mounts under a
given mountpoint.
mount --make-rshared mountpoint
mount --make-rslave mountpoint
mount --make-rprivate mountpoint
"mount --make-runbindable mountpoint"
The proc file system is not associated with a special device, and when mounting it, an
arbitrary keyword, such as proc can be used instead of a device specification. (The cus-
tomary choice none is less fortunate: the error message `none busy' from umount can be
confusing.)
Most devices are indicated by a file name (of a block special device), like /dev/sda1, but
there are other possibilities. For example, in the case of an NFS mount, device may look
like knuth.cwi.nl:/dir. It is possible to indicate a block special device using its vol-
ume label or UUID (see the -L and -U options below).
The file /etc/fstab (see fstab(5)), may contain lines describing what devices are usually
mounted where, using which options. This file is used in three ways:
(i) The command
mount -a [-t type] [-O optlist]
(usually given in a bootscript) causes all file systems mentioned in fstab (of the proper
type and/or having or not having the proper options) to be mounted as indicated, except
for those whose line contains the noauto keyword. Adding the -F option will make mount
fork, so that the filesystems are mounted simultaneously.
(ii) When mounting a file system mentioned in fstab, it suffices to give only the device,
or only the mount point.
(iii) Normally, only the superuser can mount file systems. However, when fstab contains
the user option on a line, anybody can mount the corresponding system.
Thus, given a line
/dev/cdrom /cd iso9660 ro,user,noauto,unhide
any user can mount the iso9660 file system found on his CDROM using the command
mount /dev/cdrom
or
mount /cd
For more details, see fstab(5). Only the user that mounted a filesystem can unmount it
again. If any user should be able to unmount, then use users instead of user in the fstab
line. The owner option is similar to the user option, with the restriction that the user
must be the owner of the special file. This may be useful e.g. for /dev/fd if a login
script makes the console user owner of this device. The group option is similar, with the
restriction that the user must be member of the group of the special file.
The programs mount and umount maintain a list of currently mounted file systems in the
file /etc/mtab. If no arguments are given to mount, this list is printed.
When the proc filesystem is mounted (say at /proc), the files /etc/mtab and /proc/mounts
have very similar contents. The former has somewhat more information, such as the mount
options used, but is not necessarily up-to-date (cf. the -n option below). It is possible
to replace /etc/mtab by a symbolic link to /proc/mounts, and especially when you have very
large numbers of mounts things will be much faster with that symlink, but some information
is lost that way, and in particular working with the loop device will be less convenient,
and using the "user" option will fail.
OPTIONS
The full set of options used by an invocation of mount is determined by first extracting
the options for the file system from the fstab table, then applying any options specified
by the -o argument, and finally applying a -r or -w option, when present.
Options available for the mount command:
-V Output version.
-h Print a help message.
-v Verbose mode.
-a Mount all filesystems (of the given types) mentioned in fstab.
-F (Used in conjunction with -a.) Fork off a new incarnation of mount for each
device. This will do the mounts on different devices or different NFS servers in
parallel. This has the advantage that it is faster; also NFS timeouts go in paral-
lel. A disadvantage is that the mounts are done in undefined order. Thus, you can-
not use this option if you want to mount both /usr and /usr/spool.
-f Causes everything to be done except for the actual system call; if it's not obvi-
ous, this ``fakes'' mounting the file system. This option is useful in conjunction
with the -v flag to determine what the mount command is trying to do. It can also
be used to add entries for devices that were mounted earlier with the -n option.
The -f option checks for existing record in /etc/mtab and fails when the record
already exists (with regular non-fake mount, this check is done by kernel).
-i Don't call the /sbin/mount.<filesystem> helper even if it exists.
-l Add the ext2, ext3 and XFS labels in the mount output. Mount must have permission
to read the disk device (e.g. be suid root) for this to work. One can set such a
label for ext2 or ext3 using the e2label(8) utility, or for XFS using xfs_admin(8),
or for reiserfs using reiserfstune(8).
-n Mount without writing in /etc/mtab. This is necessary for example when /etc is on
a read-only file system.
-p num In case of a loop mount with encryption, read the passphrase from file descriptor
num instead of from the terminal.
-s Tolerate sloppy mount options rather than failing. This will ignore mount options
not supported by a filesystem type. Not all filesystems support this option. This
option exists for support of the Linux autofs-based automounter.
-r Mount the file system read-only. A synonym is -o ro.
-w Mount the file system read/write. This is the default. A synonym is -o rw.
-L label
Mount the partition that has the specified label.
-U uuid
Mount the partition that has the specified uuid. These two options require the
file /proc/partitions (present since Linux 2.1.116) to exist.
-t vfstype
The argument following the -t is used to indicate the file system type. The file
system types which are currently supported include: adfs, affs, autofs, cifs, coda,
coherent, cramfs, debugfs, devpts, efs, ext, ext2, ext3, hfs, hfsplus, hpfs,
iso9660, jfs, minix, msdos, ncpfs, nfs, nfs4, ntfs, proc, qnx4, ramfs, reiserfs,
romfs, smbfs, sysv, tmpfs, udf, ufs, umsdos, usbfs, vfat, xenix, xfs, xiafs. Note
that coherent, sysv and xenix are equivalent and that xenix and coherent will be
removed at some point in the future -- use sysv instead. Since kernel version
2.1.21 the types ext and xiafs do not exist anymore. Earlier, usbfs was known as
usbdevfs. Note, the real list of all supported filesystems depends on your kernel.
For most types all the mount program has to do is issue a simple mount(2) system
call, and no detailed knowledge of the filesystem type is required. For a few
types however (like nfs, nfs4, cifs, smbfs, ncpfs) ad hoc code is necessary. The
nfs, nfs4, cifs, smbfs, and ncpfs have a separate mount program. In order to make
it possible to treat all types in a uniform way, mount will execute the program
/sbin/mount.TYPE (if that exists) when called with type TYPE. Since various ver-
sions of the smbmount program have different calling conventions, /sbin/mount.smbfs
may have to be a shell script that sets up the desired call.
If no -t option is given, or if the auto type is specified, mount will try to guess
the desired type. Mount uses the blkid or volume_id library for guessing the
filesystem type; if that does not turn up anything that looks familiar, mount will
try to read the file /etc/filesystems, or, if that does not exist, /proc/filesys-
tems. All of the filesystem types listed there will be tried, except for those
that are labeled "nodev" (e.g., devpts, proc and nfs). If /etc/filesystems ends in
a line with a single * only, mount will read /proc/filesystems afterwards.
The auto type may be useful for user-mounted floppies. Creating a file
/etc/filesystems can be useful to change the probe order (e.g., to try vfat before
msdos or ext3 before ext2) or if you use a kernel module autoloader. Warning: the
probing uses a heuristic (the presence of appropriate `magic'), and could recognize
the wrong filesystem type, possibly with catastrophic consequences. If your data is
valuable, don't ask mount to guess.
More than one type may be specified in a comma separated list. The list of file
system types can be prefixed with no to specify the file system types on which no
action should be taken. (This can be meaningful with the -a option.)
For example, the command:
mount -a -t nomsdos,ext
mounts all file systems except those of type msdos and ext.
-O Used in conjunction with -a, to limit the set of filesystems to which the -a is
applied. Like -t in this regard except that it is useless except in the context of
-a. For example, the command:
mount -a -O no_netdev
mounts all file systems except those which have the option _netdev specified in the
options field in the /etc/fstab file.
It is different from -t in that each option is matched exactly; a leading no at the
beginning of one option does not negate the rest.
The -t and -O options are cumulative in effect; that is, the command
mount -a -t ext2 -O _netdev
mounts all ext2 filesystems with the _netdev option, not all filesystems that are
either ext2 or have the _netdev option specified.
-o Options are specified with a -o flag followed by a comma separated string of
options. Some of these options are only useful when they appear in the /etc/fstab
file. The following options apply to any file system that is being mounted (but
not every file system actually honors them - e.g., the sync option today has effect
only for ext2, ext3, fat, vfat and ufs):
async All I/O to the file system should be done asynchronously.
atime Update inode access time for each access. This is the default.
auto Can be mounted with the -a option.
defaults
Use default options: rw, suid, dev, exec, auto, nouser, and async.
dev Interpret character or block special devices on the file system.
exec Permit execution of binaries.
group Allow an ordinary (i.e., non-root) user to mount the file system if one of
his groups matches the group of the device. This option implies the options
nosuid and nodev (unless overridden by subsequent options, as in the option
line group,dev,suid).
encryption
Specifies an encryption algorithm to use. Used in conjunction with the loop
option.
keybits
Specifies the key size to use for an encryption algorithm. Used in conjunc-
tion with the loop and encryption options.
mand Allow mandatory locks on this filesystem. See fcntl(2).
_netdev
The filesystem resides on a device that requires network access (used to
prevent the system from attempting to mount these filesystems until the net-
work has been enabled on the system).
noatime
Do not update inode access times on this file system (e.g, for faster access
on the news spool to speed up news servers).
nodiratime
Do not update directory inode access times on this filesystem.
relatime
Update inode access times relative to modify or change time. Access time is
only updated if the previous access time was earlier than the current modify
or change time. (Similar to noatime, but doesn't break mutt or other appli-
cations that need to know if a file has been read since the last time it was
modified.)
noauto Can only be mounted explicitly (i.e., the -a option will not cause the file
system to be mounted).
nodev Do not interpret character or block special devices on the file system.
noexec Do not allow direct execution of any binaries on the mounted file system.
(Until recently it was possible to run binaries anyway using a command like
/lib/ld*.so /mnt/binary. This trick fails since Linux 2.4.25 / 2.6.0.)
nomand Do not allow mandatory locks on this filesystem.
nosuid Do not allow set-user-identifier or set-group-identifier bits to take
effect. (This seems safe, but is in fact rather unsafe if you have suid-
perl(1) installed.)
nouser Forbid an ordinary (i.e., non-root) user to mount the file system. This is
the default.
owner Allow an ordinary (i.e., non-root) user to mount the file system if he is
the owner of the device. This option implies the options nosuid and nodev
(unless overridden by subsequent options, as in the option line
owner,dev,suid).
remount
Attempt to remount an already-mounted file system. This is commonly used to
change the mount flags for a file system, especially to make a readonly file
system writeable. It does not change device or mount point.
ro Mount the file system read-only.
rw Mount the file system read-write.
suid Allow set-user-identifier or set-group-identifier bits to take effect.
sync All I/O to the file system should be done synchronously. In case of media
with limited number of write cycles (e.g. some flash drives) "sync" may
cause life-cycle shortening.
dirsync
All directory updates within the file system should be done synchronously.
This affects the following system calls: creat, link, unlink, symlink,
mkdir, rmdir, mknod and rename.
user Allow an ordinary user to mount the file system. The name of the mounting
user is written to mtab so that he can unmount the file system again. This
option implies the options noexec, nosuid, and nodev (unless overridden by
subsequent options, as in the option line user,exec,dev,suid).
users Allow every user to mount and unmount the file system. This option implies
the options noexec, nosuid, and nodev (unless overridden by subsequent
options, as in the option line users,exec,dev,suid).
context=context, fscontext=context and defcontext=context
The context= option is useful when mounting filesystems that do not support
extended attributes, such as a floppy or hard disk formatted with VFAT, or
systems that are not normally running under SELinux, such as an ext3 format-
ted disk from a non-SELinux workstation. You can also use context= on
filesystems you do not trust, such as a floppy. It also helps in compatibil-
ity with xattr-supporting filesystems on earlier 2.4.<x> kernel versions.
Even where xattrs are supported, you can save time not having to label every
file by assigning the entire disk one security context.
A commonly used option for removable media is context=sys-
tem_u:object_r:removable_t.
Two other options are fscontext= and defcontext=, both of which are mutually
exclusive of the context option. This means you can use fscontext and def-
context with each other, but neither can be used with context.
The fscontext= option works for all filesystems, regardless of their xattr
support. The fscontext option sets the overarching filesystem label to a
specific security context. This filesystem label is separate from the indi-
vidual labels on the files. It represents the entire filesystem for certain
kinds of permission checks, such as during mount or file creation. Individ-
ual file labels are still obtained from the xattrs on the files themselves.
The context option actually sets the aggregate context that fscontext pro-
vides, in addition to supplying the same label for individual files.
You can set the default security context for unlabeled files using defcon-
text= option. This overrides the value set for unlabeled files in the policy
and requires a file system that supports xattr labeling.
For more details see selinux(8)
--bind Remount a subtree somewhere else (so that its contents are available in both
places). See above.
--move Move a subtree to some other place. See above.
FILESYSTEM SPECIFIC MOUNT OPTIONS
The following options apply only to certain file systems. We sort them by file system.
They all follow the -o flag.
What options are supported depends a bit on the running kernel. More info may be found in
the kernel source subdirectory Documentation/filesystems.
Mount options for adfs
uid=value and gid=value
Set the owner and group of the files in the file system (default: uid=gid=0).
ownmask=value and othmask=value
Set the permission mask for ADFS 'owner' permissions and 'other' permissions,
respectively (default: 0700 and 0077, respectively). See also /usr/src/linux/Docu-
mentation/filesystems/adfs.txt.
Mount options for affs
uid=value and gid=value
Set the owner and group of the root of the file system (default: uid=gid=0, but
with option uid or gid without specified value, the uid and gid of the current
process are taken).
setuid=value and setgid=value
Set the owner and group of all files.
mode=value
Set the mode of all files to value & 0777 disregarding the original permissions.
Add search permission to directories that have read permission. The value is given
in octal.
protect
Do not allow any changes to the protection bits on the file system.
usemp Set uid and gid of the root of the file system to the uid and gid of the mount
point upon the first sync or umount, and then clear this option. Strange...
verbose
Print an informational message for each successful mount.
prefix=string
Prefix used before volume name, when following a link.
volume=string
Prefix (of length at most 30) used before '/' when following a symbolic link.
reserved=value
(Default: 2.) Number of unused blocks at the start of the device.
root=value
Give explicitly the location of the root block.
bs=value
Give blocksize. Allowed values are 512, 1024, 2048, 4096.
grpquota / noquota / quota / usrquota
These options are accepted but ignored. (However, quota utilities may react to
such strings in /etc/fstab.)
Mount options for cifs
See the options section of the mount.cifs(8) man page (smbfs package must be installed).
Mount options for coherent
None.
Mount options for debugfs
The debugfs file system is a pseudo file system, traditionally mounted on /sys/ker-
nel/debug. There are no mount options.
Mount options for devpts
The devpts file system is a pseudo file system, traditionally mounted on /dev/pts. In
order to acquire a pseudo terminal, a process opens /dev/ptmx; the number of the pseudo
terminal is then made available to the process and the pseudo terminal slave can be
accessed as /dev/pts/<number>.
uid=value and gid=value
This sets the owner or the group of newly created PTYs to the specified values.
When nothing is specified, they will be set to the UID and GID of the creating pro-
cess. For example, if there is a tty group with GID 5, then gid=5 will cause newly
created PTYs to belong to the tty group.
mode=value
Set the mode of newly created PTYs to the specified value. The default is 0600. A
value of mode=620 and gid=5 makes "mesg y" the default on newly created PTYs.
Mount options for ext
None. Note that the `ext' file system is obsolete. Don't use it. Since Linux version
2.1.21 extfs is no longer part of the kernel source.
Mount options for ext2
The `ext2' file system is the standard Linux file system. Since Linux 2.5.46, for most
mount options the default is determined by the filesystem superblock. Set them with
tune2fs(8).
acl / noacl
Support POSIX Access Control Lists (or not).
bsddf / minixdf
Set the behaviour for the statfs system call. The minixdf behaviour is to return in
the f_blocks field the total number of blocks of the file system, while the bsddf
behaviour (which is the default) is to subtract the overhead blocks used by the
ext2 file system and not available for file storage. Thus
% mount /k -o minixdf; df /k; umount /k
Filesystem 1024-blocks Used Available Capacity Mounted on
/dev/sda6 2630655 86954 2412169 3% /k
% mount /k -o bsddf; df /k; umount /k
Filesystem 1024-blocks Used Available Capacity Mounted on
/dev/sda6 2543714 13 2412169 0% /k
(Note that this example shows that one can add command line options to the options given
in /etc/fstab.)
check=none / nocheck
No checking is done at mount time. This is the default. This is fast. It is wise
to invoke e2fsck(8) every now and then, e.g. at boot time.
debug Print debugging info upon each (re)mount.
errors=continue / errors=remount-ro / errors=panic
Define the behaviour when an error is encountered. (Either ignore errors and just
mark the file system erroneous and continue, or remount the file system read-only,
or panic and halt the system.) The default is set in the filesystem superblock,
and can be changed using tune2fs(8).
grpid or bsdgroups / nogrpid or sysvgroups
These options define what group id a newly created file gets. When grpid is set,
it takes the group id of the directory in which it is created; otherwise (the
default) it takes the fsgid of the current process, unless the directory has the
setgid bit set, in which case it takes the gid from the parent directory, and also
gets the setgid bit set if it is a directory itself.
grpquota / noquota / quota / usrquota
These options are accepted but ignored.
nobh Do not attach buffer_heads to file pagecache. (Since 2.5.49.)
nouid32
Disables 32-bit UIDs and GIDs. This is for interoperability with older kernels
which only store and expect 16-bit values.
oldalloc or orlov
Use old allocator or Orlov allocator for new inodes. Orlov is default.
resgid=n and resuid=n
The ext2 file system reserves a certain percentage of the available space (by
default 5%, see mke2fs(8) and tune2fs(8)). These options determine who can use the
reserved blocks. (Roughly: whoever has the specified uid, or belongs to the speci-
fied group.)
sb=n Instead of block 1, use block n as superblock. This could be useful when the
filesystem has been damaged. (Earlier, copies of the superblock would be made
every 8192 blocks: in block 1, 8193, 16385, ... (and one got thousands of copies on
a big filesystem). Since version 1.08, mke2fs has a -s (sparse superblock) option
to reduce the number of backup superblocks, and since version 1.15 this is the
default. Note that this may mean that ext2 filesystems created by a recent mke2fs
cannot be mounted r/w under Linux 2.0.*.) The block number here uses 1k units.
Thus, if you want to use logical block 32768 on a filesystem with 4k blocks, use
"sb=131072".
user_xattr / nouser_xattr
Support "user." extended attributes (or not).
Mount options for ext3
The `ext3' file system is a version of the ext2 file system which has been enhanced with
journalling. It supports the same options as ext2 as well as the following additions:
journal=update
Update the ext3 file system's journal to the current format.
journal=inum
When a journal already exists, this option is ignored. Otherwise, it specifies the
number of the inode which will represent the ext3 file system's journal file; ext3
will create a new journal, overwriting the old contents of the file whose inode
number is inum.
noload Do not load the ext3 file system's journal on mounting.
data=journal / data=ordered / data=writeback
Specifies the journalling mode for file data. Metadata is always journaled. To
use modes other than ordered on the root file system, pass the mode to the kernel
as boot parameter, e.g. rootflags=data=journal.
journal
All data is committed into the journal prior to being written into the main
file system.
ordered
This is the default mode. All data is forced directly out to the main file
system prior to its metadata being committed to the journal.
writeback
Data ordering is not preserved - data may be written into the main file sys-
tem after its metadata has been committed to the journal. This is rumoured
to be the highest-throughput option. It guarantees internal file system
integrity, however it can allow old data to appear in files after a crash
and journal recovery.
commit=nrsec
Sync all data and metadata every nrsec seconds. The default value is 5 seconds.
Zero means default.
user_xattr
Enable Extended User Attributes. See the attr(5) manual page.
acl Enable POSIX Access Control Lists. See the acl(5) manual page.
Mount options for fat
(Note: fat is not a separate filesystem, but a common part of the msdos, umsdos and vfat
filesystems.)
blocksize=512 / blocksize=1024 / blocksize=2048
Set blocksize (default 512).
uid=value and gid=value
Set the owner and group of all files. (Default: the uid and gid of the current
process.)
umask=value
Set the umask (the bitmask of the permissions that are not present). The default is
the umask of the current process. The value is given in octal.
dmask=value
Set the umask applied to directories only. The default is the umask of the current
process. The value is given in octal.
fmask=value
Set the umask applied to regular files only. The default is the umask of the cur-
rent process. The value is given in octal.
check=value
Three different levels of pickyness can be chosen:
r[elaxed]
Upper and lower case are accepted and equivalent, long name parts are trun-
cated (e.g. verylongname.foobar becomes verylong.foo), leading and embedded
spaces are accepted in each name part (name and extension).
n[ormal]
Like "relaxed", but many special characters (*, ?, <, spaces, etc.) are
rejected. This is the default.
s[trict]
Like "normal", but names may not contain long parts and special characters
that are sometimes used on Linux, but are not accepted by MS-DOS are
rejected. (+, =, spaces, etc.)
codepage=value
Sets the codepage for converting to shortname characters on FAT and VFAT filesys-
tems. By default, codepage 437 is used.
conv=b[inary] / conv=t[ext] / conv=a[uto]
The fat file system can perform CRLF<-->NL (MS-DOS text format to UNIX text format)
conversion in the kernel. The following conversion modes are available:
binary no translation is performed. This is the default.
text CRLF<-->NL translation is performed on all files.
auto CRLF<-->NL translation is performed on all files that don't have a "well-
known binary" extension. The list of known extensions can be found at the
beginning of fs/fat/misc.c (as of 2.0, the list is: exe, com, bin, app, sys,
drv, ovl, ovr, obj, lib, dll, pif, arc, zip, lha, lzh, zoo, tar, z, arj, tz,
taz, tzp, tpz, gz, tgz, deb, gif, bmp, tif, gl, jpg, pcx, tfm, vf, gf, pk,
pxl, dvi).
Programs that do computed lseeks won't like in-kernel text conversion. Several
people have had their data ruined by this translation. Beware!
For file systems mounted in binary mode, a conversion tool (fromdos/todos) is
available.
cvf_format=module
Forces the driver to use the CVF (Compressed Volume File) module cvf_module instead
of auto-detection. If the kernel supports kmod, the cvf_format=xxx option also con-
trols on-demand CVF module loading.
cvf_option=option
Option passed to the CVF module.
debug Turn on the debug flag. A version string and a list of file system parameters will
be printed (these data are also printed if the parameters appear to be inconsis-
tent).
fat=12 / fat=16 / fat=32
Specify a 12, 16 or 32 bit fat. This overrides the automatic FAT type detection
routine. Use with caution!
iocharset=value
Character set to use for converting between 8 bit characters and 16 bit Unicode
characters. The default is iso8859-1. Long filenames are stored on disk in Unicode
format.
quiet Turn on the quiet flag. Attempts to chown or chmod files do not return errors,
although they fail. Use with caution!
sys_immutable, showexec, dots, nodots, dotsOK=[yes|no]
Various misguided attempts to force Unix or DOS conventions onto a FAT file system.
Mount options for hfs
creator=cccc, type=cccc
Set the creator/type values as shown by the MacOS finder used for creating new
files. Default values: '????'.
uid=n, gid=n
Set the owner and group of all files. (Default: the uid and gid of the current
process.)
dir_umask=n, file_umask=n, umask=n
Set the umask used for all directories, all regular files, or all files and direc-
tories. Defaults to the umask of the current process.
session=n
Select the CDROM session to mount. Defaults to leaving that decision to the CDROM
driver. This option will fail with anything but a CDROM as underlying device.
part=n Select partition number n from the device. Only makes sense for CDROMS. Defaults
to not parsing the partition table at all.
quiet Don't complain about invalid mount options.
Mount options for hpfs
uid=value and gid=value
Set the owner and group of all files. (Default: the uid and gid of the current pro-
cess.)
umask=value
Set the umask (the bitmask of the permissions that are not present). The default is
the umask of the current process. The value is given in octal.
case=lower / case=asis
Convert all files names to lower case, or leave them. (Default: case=lower.)
conv=binary / conv=text / conv=auto
For conv=text, delete some random CRs (in particular, all followed by NL) when
reading a file. For conv=auto, choose more or less at random between conv=binary
and conv=text. For conv=binary, just read what is in the file. This is the
default.
nocheck
Do not abort mounting when certain consistency checks fail.
Mount options for iso9660
ISO 9660 is a standard describing a filesystem structure to be used on CD-ROMs. (This
filesystem type is also seen on some DVDs. See also the udf filesystem.)
Normal iso9660 filenames appear in a 8.3 format (i.e., DOS-like restrictions on filename
length), and in addition all characters are in upper case. Also there is no field for
file ownership, protection, number of links, provision for block/character devices, etc.
Rock Ridge is an extension to iso9660 that provides all of these unix like features.
Basically there are extensions to each directory record that supply all of the additional
information, and when Rock Ridge is in use, the filesystem is indistinguishable from a
normal UNIX file system (except that it is read-only, of course).
norock Disable the use of Rock Ridge extensions, even if available. Cf. map.
nojoliet
Disable the use of Microsoft Joliet extensions, even if available. Cf. map.
check=r[elaxed] / check=s[trict]
With check=relaxed, a filename is first converted to lower case before doing the
lookup. This is probably only meaningful together with norock and map=normal.
(Default: check=strict.)
uid=value and gid=value
Give all files in the file system the indicated user or group id, possibly overrid-
ing the information found in the Rock Ridge extensions. (Default: uid=0,gid=0.)
map=n[ormal] / map=o[ff] / map=a[corn]
For non-Rock Ridge volumes, normal name translation maps upper to lower case ASCII,
drops a trailing `;1', and converts `;' to `.'. With map=off no name translation
is done. See norock. (Default: map=normal.) map=acorn is like map=normal but also
apply Acorn extensions if present.
mode=value
For non-Rock Ridge volumes, give all files the indicated mode. (Default: read per-
mission for everybody.) Since Linux 2.1.37 one no longer needs to specify the mode
in decimal. (Octal is indicated by a leading 0.)
unhide Also show hidden and associated files. (If the ordinary files and the associated
or hidden files have the same filenames, this may make the ordinary files inacces-
sible.)
block=[512|1024|2048]
Set the block size to the indicated value. (Default: block=1024.)
conv=a[uto] / conv=b[inary] / conv=m[text] / conv=t[ext]
(Default: conv=binary.) Since Linux 1.3.54 this option has no effect anymore.
(And non-binary settings used to be very dangerous, possibly leading to silent data
corruption.)
cruft If the high byte of the file length contains other garbage, set this mount option
to ignore the high order bits of the file length. This implies that a file cannot
be larger than 16MB.
session=x
Select number of session on multisession CD. (Since 2.3.4.)
sbsector=xxx
Session begins from sector xxx. (Since 2.3.4.)
The following options are the same as for vfat and specifying them only makes sense when
using discs encoded using Microsoft's Joliet extensions.
iocharset=value
Character set to use for converting 16 bit Unicode characters on CD to 8 bit char-
acters. The default is iso8859-1.
utf8 Convert 16 bit Unicode characters on CD to UTF-8.
Mount options for jfs
iocharset=name
Character set to use for converting from Unicode to ASCII. The default is to do no
conversion. Use iocharset=utf8 for UTF8 translations. This requires CON-
FIG_NLS_UTF8 to be set in the kernel .config file.
resize=value
Resize the volume to value blocks. JFS only supports growing a volume, not shrink-
ing it. This option is only valid during a remount, when the volume is mounted
read-write. The resize keyword with no value will grow the volume to the full size
of the partition.
nointegrity
Do not write to the journal. The primary use of this option is to allow for higher
performance when restoring a volume from backup media. The integrity of the volume
is not guaranteed if the system abnormally abends.
integrity
Default. Commit metadata changes to the journal. Use this option to remount a
volume where the nointegrity option was previously specified in order to restore
normal behavior.
errors=continue / errors=remount-ro / errors=panic
Define the behaviour when an error is encountered. (Either ignore errors and just
mark the file system erroneous and continue, or remount the file system read-only,
or panic and halt the system.)
noquota / quota / usrquota / grpquota
These options are accepted but ignored.
Mount options for minix
None.
Mount options for msdos
See mount options for fat. If the msdos file system detects an inconsistency, it reports
an error and sets the file system read-only. The file system can be made writeable again
by remounting it.
Mount options for ncpfs
Just like nfs, the ncpfs implementation expects a binary argument (a struct
ncp_mount_data) to the mount system call. This argument is constructed by ncpmount(8) and
the current version of mount (2.12) does not know anything about ncpfs.
Mount options for nfs and nfs4
See the options section of the nfs(5) man page (nfs-common package must be installed).
The nfs and nfs4 implementation expects a binary argument (a struct nfs_mount_data) to the
mount system call. This argument is constructed by mount.nfs(8) and the current version of
mount (2.13) does not know anything about nfs and nfs4.
Mount options for ntfs
iocharset=name
Character set to use when returning file names. Unlike VFAT, NTFS suppresses names
that contain unconvertible characters. Deprecated.
nls=name
New name for the option earlier called iocharset.
utf8 Use UTF-8 for converting file names.
uni_xlate=[0|1|2]
For 0 (or `no' or `false'), do not use escape sequences for unknown Unicode charac-
ters. For 1 (or `yes' or `true') or 2, use vfat-style 4-byte escape sequences
starting with ":". Here 2 give a little-endian encoding and 1 a byteswapped bigen-
dian encoding.
posix=[0|1]
If enabled (posix=1), the file system distinguishes between upper and lower case.
The 8.3 alias names are presented as hard links instead of being suppressed.
uid=value, gid=value and umask=value
Set the file permission on the filesystem. The umask value is given in octal. By
default, the files are owned by root and not readable by somebody else.
Mount options for proc
uid=value and gid=value
These options are recognized, but have no effect as far as I can see.
Mount options for ramfs
Ramfs is a memory based filesystem. Mount it and you have it. Unmount it and it is gone.
Present since Linux 2.3.99pre4. There are no mount options.
Mount options for reiserfs
Reiserfs is a journaling filesystem. The reiserfs mount options are more fully described
at http://www.namesys.com/mount-options.html.
conv Instructs version 3.6 reiserfs software to mount a version 3.5 file system, using
the 3.6 format for newly created objects. This file system will no longer be com-
patible with reiserfs 3.5 tools.
hash=rupasov / hash=tea / hash=r5 / hash=detect
Choose which hash function reiserfs will use to find files within directories.
rupasov
A hash invented by Yury Yu. Rupasov. It is fast and preserves locality,
mapping lexicographically close file names to close hash values. This
option should not be used, as it causes a high probability of hash colli-
sions.
tea A Davis-Meyer function implemented by Jeremy Fitzhardinge. It uses hash
permuting bits in the name. It gets high randomness and, therefore, low
probability of hash collisions at some CPU cost. This may be used if EHASH-
COLLISION errors are experienced with the r5 hash.
r5 A modified version of the rupasov hash. It is used by default and is the
best choice unless the file system has huge directories and unusual file-
name patterns.
detect Instructs mount to detect which hash function is in use by examining the
file system being mounted, and to write this information into the reiserfs
superblock. This is only useful on the first mount of an old format file
system.
hashed_relocation
Tunes the block allocator. This may provide performance improvements in some situa-
tions.
no_unhashed_relocation
Tunes the block allocator. This may provide performance improvements in some situa-
tions.
noborder
Disable the border allocator algorithm invented by Yury Yu. Rupasov. This may pro-
vide performance improvements in some situations.
nolog Disable journalling. This will provide slight performance improvements in some sit-
uations at the cost of losing reiserfs's fast recovery from crashes. Even with
this option turned on, reiserfs still performs all journalling operations, save for
actual writes into its journalling area. Implementation of nolog is a work in
progress.
notail By default, reiserfs stores small files and `file tails' directly into its tree.
This confuses some utilities such as LILO(8). This option is used to disable pack-
ing of files into the tree.
replayonly
Replay the transactions which are in the journal, but do not actually mount the
file system. Mainly used by reiserfsck.
resize=number
A remount option which permits online expansion of reiserfs partitions. Instructs
reiserfs to assume that the device has number blocks. This option is designed for
use with devices which are under logical volume management (LVM). There is a spe-
cial resizer utility which can be obtained from ftp://ftp.namesys.com/pub/reiserf-
sprogs.
user_xattr
Enable Extended User Attributes. See the attr(5) manual page.
acl Enable POSIX Access Control Lists. See the acl(5) manual page.
Mount options for romfs
None.
Mount options for smbfs
Just like nfs, the smbfs implementation expects a binary argument (a struct
smb_mount_data) to the mount system call. This argument is constructed by smbmount(8) and
the current version of mount (2.12) does not know anything about smbfs.
Mount options for sysv
None.
Mount options for tmpfs
The following parameters accept a suffix k, m or g for Ki, Mi, Gi (binary kilo, mega and
giga) and can be changed on remount.
size=nbytes
Override default maximum size of the filesystem. The size is given in bytes, and
rounded down to entire pages. The default is half of the memory.
nr_blocks=
Set number of blocks.
nr_inodes=
Set number of inodes.
mode= Set initial permissions of the root directory.
Mount options for udf
udf is the "Universal Disk Format" filesystem defined by the Optical Storage Technology
Association, and is often used for DVD-ROM. See also iso9660.
gid= Set the default group.
umask= Set the default umask. The value is given in octal.
uid= Set the default user.
unhide Show otherwise hidden files.
undelete
Show deleted files in lists.
nostrict
Unset strict conformance.
iocharset
Set the NLS character set.
bs= Set the block size. (May not work unless 2048.)
novrs Skip volume sequence recognition.
session=
Set the CDROM session counting from 0. Default: last session.
anchor=
Override standard anchor location. Default: 256.
volume=
Override the VolumeDesc location. (unused)
partition=
Override the PartitionDesc location. (unused)
lastblock=
Set the last block of the filesystem.
fileset=
Override the fileset block location. (unused)
rootdir=
Override the root directory location. (unused)
Mount options for ufs
ufstype=value
UFS is a file system widely used in different operating systems. The problem are
differences among implementations. Features of some implementations are undocu-
mented, so its hard to recognize the type of ufs automatically. That's why the
user must specify the type of ufs by mount option. Possible values are:
old Old format of ufs, this is the default, read only. (Don't forget to give
the -r option.)
44bsd For filesystems created by a BSD-like system (NetBSD,FreeBSD,OpenBSD).
sun For filesystems created by SunOS or Solaris on Sparc.
sunx86 For filesystems created by Solaris on x86.
hp For filesystems created by HP-UX, read-only.
nextstep
For filesystems created by NeXTStep (on NeXT station) (currently read only).
nextstep-cd
For NextStep CDROMs (block_size == 2048), read-only.
openstep
For filesystems created by OpenStep (currently read only). The same
filesystem type is also used by Mac OS X.
onerror=value
Set behaviour on error:
panic If an error is encountered, cause a kernel panic.
[lock|umount|repair]
These mount options don't do anything at present; when an error is encoun-
tered only a console message is printed.
Mount options for umsdos
See mount options for msdos. The dotsOK option is explicitly killed by umsdos.
Mount options for vfat
First of all, the mount options for fat are recognized. The dotsOK option is explicitly
killed by vfat. Furthermore, there are
uni_xlate
Translate unhandled Unicode characters to special escaped sequences. This lets you
backup and restore filenames that are created with any Unicode characters. Without
this option, a '?' is used when no translation is possible. The escape character is
':' because it is otherwise illegal on the vfat filesystem. The escape sequence
that gets used, where u is the unicode character, is: ':', (u & 0x3f), ((u>>6) &
0x3f), (u>>12).
posix Allow two files with names that only differ in case.
nonumtail
First try to make a short name without sequence number, before trying name~num.ext.
utf8 UTF8 is the filesystem safe 8-bit encoding of Unicode that is used by the console.
It can be be enabled for the filesystem with this option. If `uni_xlate' gets set,
UTF8 gets disabled.
shortname=[lower|win95|winnt|mixed]
Defines the behaviour for creation and display of filenames which fit into 8.3
characters. If a long name for a file exists, it will always be preferred display.
There are four modes:
lower Force the short name to lower case upon display; store a long name when the
short name is not all upper case.
win95 Force the short name to upper case upon display; store a long name when the
short name is not all upper case.
winnt Display the shortname as is; store a long name when the short name is not
all lower case or all upper case.
mixed Display the short name as is; store a long name when the short name is not
all upper case.
The default is "lower".
Mount options for usbfs
devuid=uid and devgid=gid and devmode=mode
Set the owner and group and mode of the device files in the usbfs file system
(default: uid=gid=0, mode=0644). The mode is given in octal.
busuid=uid and busgid=gid and busmode=mode
Set the owner and group and mode of the bus directories in the usbfs file system
(default: uid=gid=0, mode=0555). The mode is given in octal.
listuid=uid and listgid=gid and listmode=mode
Set the owner and group and mode of the file devices (default: uid=gid=0,
mode=0444). The mode is given in octal.
Mount options for xenix
None.
Mount options for xfs
allocsize=size
Sets the buffered I/O end-of-file preallocation size when doing delayed allocation
writeout (default size is 64KiB). Valid values for this option are page size (typ-
ically 4KiB) through to 1GiB, inclusive, in power-of-2 increments.
attr2 / noattr2
The options enable/disable (default is disabled for backward compatibility on-disk)
an "opportunistic" improvement to be made in the way inline extended attributes are
stored on-disk. When the new form is used for the first time (by setting or remov-
ing extended attributes) the on-disk superblock feature bit field will be updated
to reflect this format being in use.
barrier
Enables the use of block layer write barriers for writes into the journal and
unwritten extent conversion. This allows for drive level write caching to be
enabled, for devices that support write barriers.
dmapi Enable the DMAPI (Data Management API) event callouts. Use with the mtpt option.
grpid / bsdgroups and nogrpid / sysvgroups
These options define what group ID a newly created file gets. When grpid is set,
it takes the group ID of the directory in which it is created; otherwise (the
default) it takes the fsgid of the current process, unless the directory has the
setgid bit set, in which case it takes the gid from the parent directory, and also
gets the setgid bit set if it is a directory itself.
ihashsize=value
Sets the number of hash buckets available for hashing the in-memory inodes of the
specified mount point. If a value of zero is used, the value selected by the
default algorithm will be displayed in /proc/mounts.
ikeep / noikeep
When inode clusters are emptied of inodes, keep them around on the disk (ikeep) -
this is the traditional XFS behaviour and is still the default for now. Using the
noikeep option, inode clusters are returned to the free space pool.
inode64
Indicates that XFS is allowed to create inodes at any location in the filesystem,
including those which will result in inode numbers occupying more than 32 bits of
significance. This is provided for backwards compatibility, but causes problems
for backup applications that cannot handle large inode numbers.
largeio / nolargeio
If nolargeio is specified, the optimal I/O reported in st_blksize by stat(2) will
be as small as possible to allow user applications to avoid inefficient read/mod-
ify/write I/O. If largeio is specified, a filesystem that has a swidth specified
will return the swidth value (in bytes) in st_blksize. If the filesystem does not
have a swidth specified but does specify an allocsize then allocsize (in bytes)
will be returned instead. If neither of these two options are specified, then
filesystem will behave as if nolargeio was specified.
logbufs=value
Set the number of in-memory log buffers. Valid numbers range from 2-8 inclusive.
The default value is 8 buffers for filesystems with a blocksize of 64KiB, 4 buffers
for filesystems with a blocksize of 32KiB, 3 buffers for filesystems with a block-
size of 16KiB and 2 buffers for all other configurations. Increasing the number of
buffers may increase performance on some workloads at the cost of the memory used
for the additional log buffers and their associated control structures.
logbsize=value
Set the size of each in-memory log buffer. Size may be specified in bytes, or in
kilobytes with a "k" suffix. Valid sizes for version 1 and version 2 logs are
16384 (16k) and 32768 (32k). Valid sizes for version 2 logs also include 65536
(64k), 131072 (128k) and 262144 (256k). The default value for machines with more
than 32MiB of memory is 32768, machines with less memory use 16384 by default.
logdev=device and rtdev=device
Use an external log (metadata journal) and/or real-time device. An XFS filesystem
has up to three parts: a data section, a log section, and a real-time section. The
real-time section is optional, and the log section can be separate from the data
section or contained within it. Refer to xfs(5).
mtpt=mountpoint
Use with the dmapi option. The value specified here will be included in the DMAPI
mount event, and should be the path of the actual mountpoint that is used.
noalign
Data allocations will not be aligned at stripe unit boundaries.
noatime
Access timestamps are not updated when a file is read.
norecovery
The filesystem will be mounted without running log recovery. If the filesystem was
not cleanly unmounted, it is likely to be inconsistent when mounted in norecovery
mode. Some files or directories may not be accessible because of this. Filesys-
tems mounted norecovery must be mounted read-only or the mount will fail.
nouuid Don't check for double mounted file systems using the file system uuid. This is
useful to mount LVM snapshot volumes.
osyncisdsync
Make O_SYNC writes implement true O_SYNC. WITHOUT this option, Linux XFS behaves
as if an osyncisdsync option is used, which will make writes to files opened with
the O_SYNC flag set behave as if the O_DSYNC flag had been used instead. This can
result in better performance without compromising data safety. However if this
option is not in effect, timestamp updates from O_SYNC writes can be lost if the
system crashes. If timestamp updates are critical, use the osyncisosync option.
uquota / usrquota / uqnoenforce / quota
User disk quota accounting enabled, and limits (optionally) enforced. Refer to
xfs_quota(8) for further details.
gquota / grpquota / gqnoenforce
Group disk quota accounting enabled and limits (optionally) enforced. Refer to
xfs_quota(8) for further details.
pquota / prjquota / pqnoenforce
Project disk quota accounting enabled and limits (optionally) enforced. Refer to
xfs_quota(8) for further details.
sunit=value and swidth=value
Used to specify the stripe unit and width for a RAID device or a stripe volume.
value must be specified in 512-byte block units. If this option is not specified
and the filesystem was made on a stripe volume or the stripe width or unit were
specified for the RAID device at mkfs time, then the mount system call will restore
the value from the superblock. For filesystems that are made directly on RAID
devices, these options can be used to override the information in the superblock if
the underlying disk layout changes after the filesystem has been created. The
swidth option is required if the sunit option has been specified, and must be a
multiple of the sunit value.
swalloc
Data allocations will be rounded up to stripe width boundaries when the current end
of file is being extended and the file size is larger than the stripe width size.
Mount options for xiafs
None. Although nothing is wrong with xiafs, it is not used much, and is not maintained.
Probably one shouldn't use it. Since Linux version 2.1.21 xiafs is no longer part of the
kernel source.
THE LOOP DEVICE
One further possible type is a mount via the loop device. For example, the command
mount /tmp/fdimage /mnt -t msdos -o loop=/dev/loop3,blocksize=1024
will set up the loop device /dev/loop3 to correspond to the file /tmp/fdimage, and then
mount this device on /mnt.
This type of mount knows about three options, namely loop, offset and encryption, that are
really options to losetup(8). If the mount requires a passphrase, you will be prompted
for one unless you specify a file descriptor to read from instead with the --pass-fd
option. (These options can be used in addition to those specific to the filesystem type.)
If no explicit loop device is mentioned (but just an option `-o loop' is given), then
mount will try to find some unused loop device and use that. If you are not so unwise as
to make /etc/mtab a symbolic link to /proc/mounts then any loop device allocated by mount
will be freed by umount. You can also free a loop device by hand, using `losetup -d', see
losetup(8).
RETURN CODES
mount has the following return codes (the bits can be ORed):
0 success
1 incorrect invocation or permissions
2 system error (out of memory, cannot fork, no more loop devices)
4 internal mount bug
8 user interrupt
16 problems writing or locking /etc/mtab
32 mount failure
64 some mount succeeded
NOTES
The syntax of external mount helpers is:
/sbin/mount.<suffix> spec dir [-sfnv] [-o options]
where the <suffix> is filesystem type and -sfnvo options have same meaning like standard
mount options.
FILES
/etc/fstab file system table
/etc/mtab table of mounted file systems
/etc/mtab~ lock file
/etc/mtab.tmp temporary file
/etc/filesystems a list of filesystem types to try
SEE ALSO
mount(2), umount(2), fstab(5), umount(8), swapon(8), nfs(5), xfs(5), e2label(8),
xfs_admin(8), mountd(8), nfsd(8), mke2fs(8), tune2fs(8), losetup(8)
BUGS
It is possible for a corrupted file system to cause a crash.
Some Linux file systems don't support -o sync and -o dirsync (the ext2, ext3, fat and vfat
file systems do support synchronous updates (a la BSD) when mounted with the sync option).
The -o remount may not be able to change mount parameters (all ext2fs-specific parameters,
except sb, are changeable with a remount, for example, but you can't change gid or umask
for the fatfs).
Mount by label or uuid will work only if your devices have the names listed in /proc/par-
titions. In particular, it may well fail if the kernel was compiled with devfs but devfs
is not mounted.
It is possible that files /etc/mtab and /proc/mounts don't match. The first file is based
only on the mount command options, but the content of the second file also depends on the
kernel and others settings (e.g. remote NFS server. In particular case the mount command
may reports unreliable information about a NFS mount point and the /proc/mounts file usu-
ally contains more reliable information.)
Checking files on NFS filesystem referenced by file descriptors (i.e. the fcntl and ioctl
families of functions) may lead to inconsistent result due to the lack of consistency
check in kernel even if noac is used.
HISTORY
A mount command existed in Version 5 AT&T UNIX.
AVAILABILITY
The mount command is part of the util-linux-ng package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
Linux 2.6 2004-12-16 MOUNT(8)
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